1. Field of the Invention
The present invention relates to a method for producing a hollow engine valve designed to have an increased strength and a reduced weight.
2. Description of the Related Art
Among engine valves, various engine valves designed as follows are recently provided along with the increase in output and performance of an engine. An inside of the engine valve is formed to be hollow and this hollow portion is filled with metallic sodium serving as a coolant. This design reduces the weight, and improves the thermal conductivity by the action of metallic sodium filled in the hollow portion, compared to a solid engine valve. A conventional method for producing such a hollow engine valve is disclosed in, for example, Patent Document 1.